Firearms are provided with a firing pin having an anvil end struck by the firearm hammer upon pulling of the trigger, when the firearm is fired. The other end of the firing pin is adapted to strike the rear of the cartridge, either at its center or proximate its edge, for firing the explosive charge in the cartridge and projecting the bullet through the firearm barrel. The firing pin has a shoulder abutment, proximate the anvil end, which limits the amount of forward motion of the firing pin upon striking of the anvil by the hammer.
In firearms designed for use with center-fire ammunition, the firing pin is in the form of a slender steel rod slidably disposed in a longitudinal bore formed in the firearm bolt. The firearm bolt is disposed in a longitudinal bore in a bolt-carrier and, generally, the assembly formed by the firing pin, the bolt and the bolt carrier is reciprocable relative to a stationary member of the firearm such as the receiver. In automatic firearms, or semi-automatic, reciprocation of the bolt and bolt-carrier in the receiver away from the firearm chamber accomplishes the functions of unlocking the bolt locking lugs from the barrel extension lugs, displacing the bolt and bolt-carrier rearwardly, and returning the hammer to the cocked position, while simultaneously extracting the cartridge of the spent round of ammunition from the chamber and ejecting the cartridge through an ejection port. The return of the bolt and bolt-carrier by the action of a return spring causes feeding of a fresh cartridge from the clip or magazine into the chamber. At the end of the stroke of the bolt-carrier, a pin and cam arrangement causes the bolt, after introducing its lugs through the lugs of the barrel extension, to rotate and lock the bolt in position, thus closing the chamber.
In gas-operated firearms, the rearward motion of the bolt-carrier in the receiver is effected by a mechanism actuated by the expansion of the gas propelling the bullet through the barrel, bypassed through a gas port disposed through the sidewall of the barrel. Some firearms are designed to permit this bled gas to expand in a cylinder between the bolt and the bolt-carrier, driving the bolt-carrier to the rear, unlocking the bolt, and causing the bolt and bolt-carrier to be propelled in a rearward direction, returning the hammer to the cocked position and compressing the bolt-carrier return spring. The compressed spring, when expanding, returns the bolt-carrier towards the chamber, picking up a fresh cartridge and locking the bolt in position in the chamber, as previously explained.
In such gas-operated firearms, considerable leakage of gas occurs between the peripheral surface of the bolt and the inner wall surface of the bolt-carrier where the rear extension of the bolt projects through the end of the bolt-carrier. The stream of leaking gas bathes the firing pin shoulder abutment and the peripheral surface of the firing pin stem between the shoulder abutment and the rear extension of the bolt. Carbon and other dirt particles are progressively deposited as a strongly adhering coating on the exposed surfaces of the firing pin, and more particularly on the peripheral surface of the stem proximate the shoulder abutment, on the lateral surface of the shoulder abutment directed toward the bolt rear extension and at the junction between the peripheral surface of the stem and the shoulder abutment lateral surface. Such carbon, and other residue, deposits may build up to the point that the firing pin becomes literally jammed or frozen in the end of the bolt bore, and/or to the point that the deposit on the lateral surface of the shoulder abutment becomes thick enough to prevent adequate stroke of the firing pin, upon hitting of its anvil end by the hammer, or sufficient force to be transmitted by the hammer to the firing pin, thus causing misfiring of the cartridge in the chamber.
The present invention provides a particular structure for firearm firing pins which remedies the inconveniences of the prior art, the particular firing pin structure of the invention preventing the accumulation of carbon or other dirt particles on the peripheral surface of the firing pin stem and shoulder abutment.